Plugging into your computer via USB, Leap Motion's 3D gesture control sensor wants to allow you to control your cursor without a keyboard or mouse.

For the last three decades, we've primarily interacted with our computers using two devices: the keyboard and mouse. Leap Motion intends to change that. Today the company begins shipping its eponymous 3D gesture control sensor, a black-and-aluminum rectangle the size of a pack of gum that lets you control your computer by waving your hands. The $80 device, winner of a 2012 Breakthrough Product Award, opens up the possibility for completely keyboard- and mouse-free computing. Right now, it's better in specific applications, like the 75 available in Leap's web-based Airspace Store. Where the device truly stands to excel, though, is not alone, but in conjunction with the tried and true inputs we're used to.

The Leap Motion's guts are nothing too fancy—two CMOS sensors and three infrared LEDs—but they provide enough data for the tracking of individual finger movements. The device plugs in via USB and is controlled mainly through Airspace, a program that looks like the Launchpad in Mac OS X and displays all the apps installed in the user's account. Those apps may be why it took so long for the Leap Motion to hit the market—at the end of 2012, it seemed like it was just a few months away. But, Leap CEO Michael Buckwald says, "it takes developers time to build content, and we really only have one chance to do this right."

He also cites "the complexity of the product," which, on the user's end, becomes apparent when getting used to physically using it. Though setup is easy (there basically is no setup), successfully controlling what's on screen is a bit more difficult. Moving a cursor with your fingers may be intuitive—it's essentially what we all do on touchscreens—but doing it in the air takes some practice. For one, there's the Leap's field of vision, which is limited by the power it can draw from USB. The bigger hurdle is getting used to interactions that have been translated, for better or worse, straight from keyboard and mouse inputs. Choosing a button that says "start" in a game, for instance, takes longer than clicking on it with a mouse; you have to hover your finger in just the right position, making sure your hand is almost impossibly steady, for a few seconds, as the program registers you're actually intending to hover your finger in that spot.

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Other interactions have been translated more successfully. In the New York Times app, for example, you browse and scroll articles by twirling a finger. In Airbeats, you flap your hands around to hit corresponding (that is, corresponding to your hand's position relative to the Leap) drums and cymbals. And moving the avatar in my favorite game so far, Out of the Blocks, is natural: A glide of the hand forward moves the character forward, a glide right moves the character right, and so on. (That game, by the way, is an abstract, trippy success: The avatar is in a world made of blocks, where some of those blocks are buildings, others are buses, and others are villains to be shot with block-bullets.)

Most of the games in the Airspace Store, like most of the applications in general, are fun for a while but end up feeling like novelties. That's not to say the Leap Motion itself is trivial, just that it'll take some time for developers to figure out how best to incorporate gesture controls into their programs. According to Buckwald, the Leap provides "the potential to democratize the more complex things you can do with a computer." In other words, it'll let more people do more. Take CAD, for instance. Autodesk has made manipulating 3D objects wildly natural on the iPad—the company compares it to sculpting with clay, and it's right—but the same doesn't quite exist on computers yet. The Leap Motion seems an ideal (if not the ideal) way to bring the user experience of molding objects on an iPad to a regular—and more powerful—computer.

What the Leap Motion is not ideal for is everything. You still need a keyboard and mouse, and that's fine, because they're really good at what they do. Likewise, the Leap Motion is really good at what it does: 3D gesture control. Sometimes, 3D gesture control is enough to be the sole input, as in Airbeats. But most of the time, it seems better used as a third input, something that works alongside the keyboard and mouse, making all three better than any single one would be alone.

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